The present invention relates to a plasma processing method and apparatus to be used for manufacture of semiconductor or other electron devices and micromachines.
In the manufacture of semiconductor or other electron devices and micromachines, thin-film processing techniques using plasma processing have been becoming increasingly important in recent years.
As an example of conventional plasma processing methods, plasma processing using a patch-antenna type plasma source is described below with reference to FIG. 5. Referring to FIG. 5, while interior of a vacuum chamber 1 is maintained to a specified pressure by introducing a specified gas from a gas supply unit 2 into the vacuum chamber 1 and simultaneously performing exhaustion by a turbo-molecular pump 3 as an exhauster, a high-frequency power of 100 MHz is supplied by an antenna use high-frequency power supply 4 to an antenna 5 provided so as to project into the vacuum chamber 1. Then, plasma is generated in the vacuum chamber 1, allowing plasma processing to be carried out with a substrate 7 placed on a substrate electrode 6. There is also provided a substrate-electrode use high-frequency power supply 8 for supplying high-frequency power to the substrate electrode 6, making it possible to control ion energy that reaches the substrate 7. The high-frequency voltage supplied to the antenna 5 is delivered to a proximity to the center of the antenna 5 by a feed bar 9. A plurality of sites of the antenna 5 other than its center and peripheries, and a face 27 of the vacuum chamber 1 opposite to the substrate 7 are short-circuited by short pins 10. A dielectric plate 11 is sandwiched between the antenna 5 and the vacuum chamber 1, and the feed bar 9 and the short pins 10 serve to connect the antenna 5 and the antenna use high-frequency power supply 4 to each other, and the antenna 5 and the vacuum chamber 1 to each other via through holes provided in the dielectric plate 11. Also, surfaces of the antenna 5 are covered with an antenna cover 15. The antenna cover 15 is fixed to the antenna 5 by bolts 25. Further, a slit 14 is provided so as to comprise a recessed or grooved space between the dielectric plate 11 and a dielectric ring 12 provided at a peripheral portion of the dielectric plate 11, and a recessed or grooved space between the antenna 5 and a conductor ring 13 provided at a peripheral portion of the antenna 5.
The turbo-molecular pump 3 and an exhaust port 19 are disposed just under the substrate electrode 6, and a pressure-regulating valve 20 for controlling the vacuum chamber 1 to a specified pressure is an up-and-down valve disposed just under the substrate electrode 6 and just over the turbo-molecular pump 3. The substrate electrode 6 is fixed to the vacuum chamber 1 with four pillars 21.
In the plasma processing described in the above prior-art example, however, plasma density would become the highest at the slit, posing an issue of damage of a bottom face 26 of the slit. The vacuum chamber, which is typically made of aluminium, is generally coated with anodic oxide (alumite) for prevention of corrosion of the inner wall surface of the vacuum chamber. However, the alumite of the slit bottom face would be damaged and, over repeated plasma processing, the alumite would become gradually thinner and thinner. According to our experiments, when the thickness of alumite was measured before and after an about 1,000 pcs. etching process, an about 10 μm decrease of film thickness was found. Shortage of the alumite thickness would lead to problems such as corrosion of base-material aluminium or occurrence of dust. For prevention of this, it is necessary to disassemble most of the plasma source unit and replace the aluminium member, which is heavy and expensive, unfortunately. Furthermore, since the antenna cover 15 is fixed to the antenna 5 by the bolts 25, deposited film resulting from the plasma processing tends to be peeled off from the vicinities of the bolts 25, causing occurrence of dust, as another problem.
Meanwhile, in the plasma processing described in the prior-art example, there is an issue that the temperature of the antenna cover 15 increases due to plasma exposure. Since the antenna cover 15 and the antenna 5 are vacuum-insulated from each other, the temperature of the antenna cover 15 gradually increases over repeated plasma processing. According to our experiments, it was found that the temperature of the antenna cover 15 increases up to 170° C. after 5-min. plasma processing and 1-min. vacuum holding is repeated six times. Such an abrupt change in the temperature of the antenna cover 15 may cause not only occurrence of dust but also cracks of the antenna cover 15.
In view of these and other prior-art issues, an object of the present invention is to provide a plasma processing method and apparatus which is less liable to occurrence of dust and cracks of the antenna cover.